In general, a receiver in a wireless communication system does not have a priori knowledge of the physical channel over which the transmitted signal propagates or the time at which a transmitter transmits the signal. Timing synchronization, also known as clock recovery, is the process by which the receiver processes a received signal to determine the precise transition points within the received waveform. In other words, the receiver attempts to “synchronize” or align its clock with the clock of the arriving waveform. This process requires the receiver to estimate or otherwise determine the appropriate “timing offset” of the received signal, i.e., the amount of skew between the transmitter's clock and that of the arriving waveform.
Incorrect determination of the timing offset can have detrimental effects on other receiver operations, such as channel estimation, symbol detection, and the like. For example, an incorrect timing offset may cause the received waveform to be sampled at times during which the waveform is in transition between two symbols resulting in an increased number of symbol detection errors.
Ultra-wideband (UWB) systems transmit information via baseband transmissions with high penetration capability and rich multipath diversity. However, the information-bearing waveforms are impulse-like and have low power, which increases the difficulty in achieving accurate and efficient timing synchronization. Timing synchronization algorithms have been developed to mitigate timing offset even in the presence of an unknown multipath channel. However, physical systems often incur residual timing errors, particularly under low complexity constraints.
On the other hand, some modulation schemes bypass channel estimation, such as transmitted reference (TR) and differential schemes. TR schemes correlate each received information-bearing waveform with a pilot waveform whereas differential schemes correlate adjacent information-bearing waveforms. Thus, differential schemes are more bandwidth efficient than TR schemes.